---
title: "Environment Variables"
icon: "gear"
---

This guide explains the key environment variables used to configure organizations in your Cal.com self-hosted instance.

## RESERVED_SUBDOMAINS

This is a comma-separated list of subdomains that are not allowed to be used as organization slugs.

For example, if you set `RESERVED_SUBDOMAINS="app,auth,help"`, then the domains `app.cal.com`, `auth.cal.com` and `help.cal.com` are reserved for use by the Cal.com instance. This means you cannot create an organization with the slug `app`, `auth` or `help`.

## ALLOWED_HOSTNAMES

This is a comma-separated list of domains on whose subdomains the booking pages and dashboard are allowed to work.

**Examples:**

If `ALLOWED_HOSTNAMES="cal.com,cal.dev"`, then:
- `acme.cal.com` is a valid organization booking domain and `WEBAPP_URL` can be set to `http://app.cal.com`
- `dunder.cal.dev` is also a valid organization subdomain and `WEBAPP_URL` can be set to `http://app.cal.dev`

If `ALLOWED_HOSTNAMES="cal.domain.tld"`, then:
- `WEBAPP_URL` should be set to `http://app.cal.domain.tld`
- Valid organization domains include: `acme.cal.domain.tld`, `dunder.cal.domain.tld`, `xxxx.cal.domain.tld`

<Info>
Make sure your DNS is properly configured to point organization subdomains to your Cal.com instance.
</Info>